Photographic silver halide emulsion



April 7,1942. o, 'IESTER 2,278,947

PHOTOGRAPHIC SILVER HALIDE EMULSIONS Filed Oct. 11. 1940 FIG. 7.

Ookac? Rieste r INVENTOR Hl-S ATTORNEYS Patented Apr. 7, 1942 UNITED STATES PATENT OFFICE 2,213,947 rnorocnarnrc snmzn HALIDE EMULSION Application October 11, 1940, Serial No. 360,771 In Germany November 13, 1939 4 Claims.

My present invention relates to photographic silver halide emulsions and more particularly to silver halide emulsions which contain compounds capable of sensitizing said emulsions.

Since Vogel has recognized that it is possible to render a silver halide emulsion sensitive to light beyond the range of .the characteristic sensitiveness of silver halide by means of an addition of a sensitizing dyestuif, a-great number of dyestuffs have been proposed for sensitizing a silver halide emulsion more or less intensively in all spectral regions. It has hitherto commonly been believed necessary that the sensitizera are dyestuffs. There is a direct relation between the absorption range 'and the sensitization range of the dyestuffs or between the absorption maximum and the sensitization maximum. The known rule expresses that the sensitization maximum is 20-40 m in special cases to 80-90 ma distant from the absorption maximum oi the dyestufi.

Besides these optical sensitizers there are chemical sensitizers the effect of which is of another kind. The chemical sensitizers only increase the natural sensitiveness of the silver halide emulsion without changing the spectral sensitiveness range.

It is one object of my invention to provide a photographic silver halide emulsion containing a compound with a rhodanine ring as a sensitizer.

Another object is the provision of a photographic emulsion containing a colorless compound with a rhodanine ring as a sensitizer.

A further object is to provide a photographic emulsion containing a colorless compound with a rhodanine ring, said compound having not the constitution of a dyestufi. e

A still further object is to provide a photographic emulsion containing a colorless compound with at least one rhodanine ring as'a sen- I sitizer.

Yet another object is the provision of a 'photographic emulsion containing a colorless com-, pound with a rhodanine ring, at least one sulfur attgm of said ring being substituted by a selenium a m.

Other objects of my invention will appear from the disclosure following hereinafter. g

Reference is made to the. accompanying drawinginwhich I I Figure 1 shows the spectral region of a silver halide emulsion not especially sensitized and- Flgure 2 shows the spectral region of a silver halide emulsion sensitized by N-ethyl-rhodanine.

The silver halide emulsions are optically sensitized in the spectral green by the compounds deiined in the statement of invention. The compounds of this kind have the following general I formula:

in which X is oxygen, sulfur or selenium,

Y and Z are sulfur or selenium,

R. is a non-substituted or substituted alkyl, al-

kylene, cyclo-alkyl, aralkyl, aryl, amino group or an N-alkylene-rhodanine ring.

Whereas all known optical sensitizers are undistillable, high-melting substances, many compounds are among the sensitizers defined above which may be distilled in vacuum, under atmospheric pressure or with steam or are even liquid at room temperature as for example N- ethyl-rhodanine'. The class of these compounds has further the great advantage that by using them undyed photographic images are obtained in contrast with the hitherto known sensitizing dyestuffs. The colorless sensitizers have a sensitization maximum and an absorption maximum which are about100-200 my. distant from each other.

The colorless rhodanine compounds may be 5 sensitization generally amount to about 1-100 mentioned.

The following examples serve to illustrate the invention but they are not intended to limit it thereto. Therhodanine compounds are generally prepared according to known processes.

Example I A silver halide emulsion sensitized with N- ethyl-rhodanine shows sensitization maxima at 500 and 550 mp.

1 Example II A silver halide emulsion sensitized with N- allyl-rhodanine shows sensitization maxima at 500 and 555 mu.

Example III A silver halide emulsion sensitized with llethylene-rhodanine, prepared for instance as mula rhoclanine,

Example IV A silver halide emulsion sensitized with N- ethyl-seleno-azolonthion made as described in Belgian Patent No. 437,921 and having the forshows a sensitization maximum at 525 my.

Further examples for compounds 01 this class are N-phemrlrhodanine, N-hydroxy-propylrhodanine, N-amino-rhodanine, N-phenyl-ethyl- N-cyclohexyl-rhodanine, and N- methyl-seleno-azolonthion the sensitization maxima ofl which are in the green.

I claim: i

1. A photographic silver halide emulsion containing as a sensitizer a compound having the following general formula:

wherein X is a member selected from the class consisting of oxygen, sulfur, and selenium: Y and Z are members selected from the class consisting of sulfur and selenium; R is a member selected from the class consisting of alkyl, alkylene, cyclo-alkyl, aralkyl, aryl, amino-group, and N- alkylene-rhodanine.

2. A photographic silver halide emulsion containing N-ethyl-rhodanine.

3. A photographic silver halide emulsion containing a compound of the following constitution:

I fk

taining a compound of the following constitution:

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